Hello Sukhvir,
According to the the AIIMS MBBS prospectus, the list of documents required at the time of admission to MBBS course at the AIIMS are-
Certificate of having passed the 10+2 or equivalent examination.
Certificate from the board from which he/she has passed the high school showing the DOB.
Marksheet of 10+2 examination
Migration certificate from the Board/University last attended.
SC/ST/OBC certificate.

Gap year certificate between 10th and 11th might not be needed. You can also contact the AIIMS authorities for further clarification.
Good Luck!